This invention relates to a wire cut electric discharge machine in which an electric discharge machining operation is carried out with a machining solution applied between the wire electrode and the workpiece, and more particularly to the control of the specific resistance of the machining solution.
FIG. 3 outlines the arrangement of a conventional wire cut electric discharge machine. In FIG. 3, reference numeral 1 designates a memory for storing various data concerning a wire cut electric discharge machining operation; 2, a paper tape input/output unit for punching a paper tape and reading the data punched in a paper tape; 3, a CRT (cathode ray tube) for displaying a variety of pieces of data; 4, a keyboard for inputting data and instructions; 5, an input/output unit for transmitting data to and receiving data from a flexible disk 6 which stores data provided through the input/output unit 5; and 7, arithmetic means for processing the data which are transferred from the flexible disk 6, through the paper tape input/output unit 2, the keyboard 4 and the input/output unit 5, and executing the operations shown in FIG. 4, a flow chart (the arithmetic means 7 is hereinafter referred to as a "CPU", when applicable). The components 1 through 7 form a numerical control device.
Further in FIG. 3, reference numeral 9 designates a specific resistance detecting unit for detecting the specific resistance of a machining solution; 10, a specific resistance control unit operating to maintain the specific resistance of a machining solution constant; 11, a specific resistance meter for indicating the specific resistance of a machining solution; 12, a data transmitting bus; 15, a wire electrode; 16, wire guides for supporting the wire electrode 15; 17, a nozzle for jetting a machining solution; 19, a machining solution used for machining; 20, a filter for a machining solution; 21, a machining solution passed through the filter 20; 22, a pump for pumping the machining solution out of a machining solution vessel 24; and 30, a wire cut electric discharge machine body.
The operation of the conventional wire cut electric discharge machine thus constructed will be described with reference to the flow chart of FIG. 4.
Prior to analysis of a numerical control program (hereinafter referred to as "an NC program", when applicable) inputted by the paper tape input/output unit 2 or inputted by the input/output unit 5 using the flexible disk 6, the CPU 7 operates to initialize the memory 1 which is used to store specific resistance specifying codes (Step S41). After the initialization of the memory 1, the CPU 7 reads the NC program from the input/output unit 5 or the paper tape input/output unit 2 (Step S42), and analyzes it line by line beginning from the first line thereby to determine whether it includes an error or not, and whether it includes codes for driving the electric discharge machine body or a specific resistance specifying code (Step S43). When an error is included, the CPU displays an error message on the CRT, to suspend the analysis (Step S44). When a specific resistance specifying code is encountered, then the CPU 7 operates to store the specific resistance thus specified in the memory 1 which has been initialized in Step S41 (Step S46). The specific resistance stored in Step S46 is applied, as a signal, to the specific resistance control unit 10. Thereafter, the CPU 7 detects the specific resistance with a sensor 18 which is provided for the specific resistance control unit 10 adapted to control the filtered machining solution, and operates to cause the specific resistance meter 11 or the CRT 3 to display the specific resistance of the filtered machining solution 21 (Step S48). Then, the CPU 7 determines whether or not the NC program step has been executed (Step S49). If the execution of the NC program step has not been accomplished yet, then the next NC program step is effected; that is, the M code for driving the electric discharge machine body is utilized, and the pump 22 is driven to jet the filtered machining solution 21 to the wire electrode 15 through the nozzle 17 (Step S50).
As was described above, in the conventional wire cut electric discharge machine, the specific resistance is displayed on the CRT or the specific resistance meter; however, the CPU does not refer to the set value for specific resistance, and the electric discharge machining operation may be started before the set value is reached. In order to overcome the difficulty, the operator must confirm that the specific resistance displayed on the specific resistance meter or the CRT has reached the set value before the machining operation is started.